Place 3 tablespoons butter in a deep, 2 quart, heat-resistant, non-metallic casserole.
Melt on full power 30 seconds.
Add steak strips to butter and heat, uncovered, on full power for 10 minutes or until meat is browned.
Add onion, mushrooms and seasoning to meat.
Heat, uncovered, on full power for 4 minutes.
Add cubed cream cheese and milk to meat mixture and heat, uncovered, on roast for 6 minutes or until cheese melts.